Synoptic analysis · mean sea-level pressure
ISOBAR — pressure you can read by the weight of the type
Air has weight, and it presses hardest where you least expect. Below is a live pressure chart: a low winding tighter over the ocean, its isobars packed like the contour lines of a cliff. The reading grows heavier as the air fills back in — and thins to a whisper as the low bites down.
Central pressure is being rendered as the weight of the numerals: the deeper the low, the lighter the reading.
Reading the chart
Lines of equal weight
Every blue loop threads points at the same pressure. Trace one and you are walking a level path across an invisible landscape of air — a contour map of the sky, drawn every four hectopascals.
4hPa per linePacked lines, hard wind
Where the isobars crowd, the pressure changes fast over a short distance — and the wind runs strong along them. Loose spacing is calm; a tight nest of rings is a gale wrapped around a centre.
×3wind per halving of spacingThe low that deepens
A falling centre is a strengthening storm; a rising one is filling and letting go. Watch the readout above lose weight as it deepens, and thicken again as the air pours back in.
−2.9hPa in three hoursPressure, printed at its own weight
A barometer answers a single question — how hard is the atmosphere leaning on this spot right now? On a paper chart that answer hides inside a number. Here it is also the weight of the numeral itself.
One variable font drives everything you read. Its weight axis is wired straight to the central pressure of the low: as the system fills toward a thousand hectopascals the digits thicken and stand up; as it deepens they slim to a hairline. You feel the storm before you finish reading it.
A deep low over open water can fall 24 hPa in 24 hours — a "bomb". On this chart that plunge is a headline shedding weight in front of you, letter by letter.
The scale above is fixed for reference. The chart's own readout moves through it continuously, live.